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Introduction

Acute kidney injury (AKI) complicates over 50% of ICU admissions. Episodes of AKI
are a major risk factor for development or progression of chronic kidney disease (CKD);
however, methods of estimated glomerular filtration rate (eGFR) may be poorly calibrated
to survivors of critical illness who may have reduced muscle mass. We hypothesized
that eGFR may underestimate rates and severity of CKD in ICU survivors.

Methods

A retrospective observational study of renal function in all patients admitted to
a London teaching hospital ICU for ≥5 days and surviving to hospital discharge in
2011. We excluded cases with current or new diagnosis of end-stage renal disease or
renal transplant. We assessed AKI in ICU by KDIGO 1 criteria and hospital discharge
eGFR by the CKD-EPI equation. For comparison we assumed a normal GFR in a healthy
individual as 120 ml/minute/1.73 m2 at age 20 decreasing by 0.8 per year over age 20.

Results

We identified 282 patients, 180 of whom had AKI. Median age was 50 and 68% were male.
Median hospital discharge serum creatinine was 573 μmol/l (range 16 to 654), median
eGFR was significantly higher than predicted normal GFR for age at 115 versus predicted
95 (P 0.001, median difference 16). In patients who had not had AKI discharge the eGFR was
119 versus normal predicted 98 (P 0.001, median difference 19), suggesting that eGFR could be overestimating true GFR
in our population by at least a factor of 1.23 (Figure 1). Applying this correction factor to eGFRs of patients who had recovered from AKI
resulted in 44% more diagnoses of CKD (eGFR <60) at hospital discharge (36 vs. 25).

Conclusion

eGFR may overestimate renal function in survivors of critical illness confounding
identification of CKD in this at-risk population. Prospective studies with measurement
of actual GFR are required to assess the burden of CKD in survivors of critical illness.